Trench cutting machines are used in a wide variety of environments and for a wide variety of purposes. One such environment is soft dirt or clay such as is frequently encountered in digging trenches for water lines or sewers or electrical lines which are buried a relatively short distance below the earth surface in a soft dirt or clay. In other environments, trenches must be cut in medium hard rock formations (i.e., formations having a compressive strength on the order of 6,000 to 12,000 psi, such as limestone and sandstone) and in extremely hard rock formations (i.e., formations having a compression strength of 25,000 psi minimum, such as diorite, granite, quartzite, or basalt).
The prior art has provided a variety of machines for cutting trenches. Certain of these prior art devices are shown in U.S. Pat. Nos. 3,219,390; 3,374,034; 3,472,555; and 3,148,917. A more recent U.S. Pat. No. 4,035,024 departs from prior art techniques of providing a hard rock trench cutting machine which is particularly well suited for use in underground mining when medium hard to extremely hard rock formations are encountered. In such mining, a vein of coal or ore which is mined may be of insufficient height to permit a mining railroad car to travel through the space which is left after the vein is mined. The hard rock trench cutting machine according to that invention is used to cut a trench through the hard rock at the bottom of the vein to provide a trench of sufficient depth to permit a mining railroad car to travel in the trench to permit removal of coal or ore from more remote locations in the vein.
A vein of coal or ore is seldom straight and any trench cutting machine must be designed with steering capability so that the operator may follow the vein. The hard rock cutting machine disclosed in U.S. Pat. No. 4,035,024 is capable of being steered by an adjustment of the hydraulic fluid in the clamping feet of the machine to thereby adjust the extension of the feet and the angle of attack on the hard rock. The operation is not particularly precise and is difficult to perform. A further drawback is that the hydraulic motors which power the cutting wheel must have a relatively short axial extent so as not to interfere with the tunnel roof. More powerful motors are available but their axial height prohibits their use in a trench cutting machine.